We can say that this Multidirectional microphone circuit consists one side of electret four modules, each of them provide power to the capsule through 10K resistor, DC blocked through 1μF capacitor and the resulting AF signal is received at the end of the potentiometer which serves as a reception setting. 100K resistors and transistors form a network FET preamp and summing several signals, which can be applied without any problems on the line input as the microphone channel of the console.

The circuit is powered by a 9V and consumption is very low, so it can be safely operated by a power source or standard 9V battery. In the latter case, remember that proper filtering is the key to good audio quality.

Output cables must be shielded types (mesh) to prevent interference or noise from the sound produced.

It is recommended to mount it in a cabinet or in a circular or pyramidal. Although the first is what gives best results and has a nice aesthetic.

Another recommendation that is not in the scheme is to put a 100nF capacitor between + V and mass within the printed circuit of the apparatus.

The potentiometer allows to adjust the sensitivity of each microphone. This is useful when there are more people on one side than another, or when someone is talking too loudly than others.

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This Simple preamplifier circuit provides sufficient gain to weak audio signals from the microphone. This circuit can also be supplied from the voltage baterry 3 to 9 volts if necessary. Take a note that the microphone used in this pre-amp circuit is electret type.

If you are using high fidelity sound system, the this mic pre-amp will not become a good choice, you should be find other circuits.

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The operating principle is as follows:
Resistors R1, R3 is used to adjust the gain, which equals 25. To increase the gain by 75 to build a resistance of 68 ohms. It is not recommended to install too high gain, because it may affect the sound quality, although this depends on the microphone. Capacitors C5 and C6 are used for suppression of feeding.

This circuit has been tried on three microphones, one from SONY, and then two Chinese, everything works! With the correct assembly of the device starts to work immediately, and does not need tuning.

Parts list :
R1, R3 : 220
R2, R4 : 1K5
R5, R6 : 6K2
R7 : 470
C1, C2, C3 : 0.1uF
C3, C4, C7, C8 : 10uF/10V
C5 : 470uF/15V
DA1 : K548UN1

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The circuit is divided into two parts. Left – is located in close proximity to the microphone, for example, in his case. The right-hand – anywhere – in the amplifier, a mixer. Connect these two pieces of two-wire, shielded cable.

How does it work? It’s very simple – a signal from a microphone, amplified the left side is fed to the right side, the input stage of which (VT3, VT4) is an accumulator with a phase shift of 180 degrees (the phase of the signal, not of what you think.) Thus, the useful signal coming out of phase two wire folded and its value is doubled. And the nasty in-phase noise are mutually self-destruct.

The input impedance amplifier – about 57 ohms. At assembly, the left side it is desirable to place a metal screen.

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Key Features

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